where \(c_{ij}\equiv \cos \theta _{ij}\)  and \(s_{ij}\equiv \sin \theta _{ij}\) .
The \(\theta _{ij}\) 's are the three real mixing parameters while
\(\delta \)  is the Kobayashi–Maskawa phase. It is known experimentally
that \(s_{13}\ll s_{23}\ll s_{12}\ll 1\) . It is convenient to choose an
approximate expression where this hierarchy is manifest. This is the
Wolfenstein parametrization, where the four mixing parameters are
\((\lambda ,A,\rho ,\eta )\)  with \(\lambda =|V_{us}|=0.23\)  playing the role
of an expansion parameter and \(\eta \)  representing the CP violating
phase [1]}, [2]}:
\(V=\begin{pmatrix}1-\frac{1}{2}\lambda ^2-\frac{1}{8}\lambda ^4 & \lambda & A\lambda ^3(\rho -i\eta )\\-\lambda +\frac{1}{2}A^2\lambda ^5[1-2(\rho +i\eta )] &1-\frac{1}{2}\lambda ^2-\frac{1}{8}\lambda ^4(1+4A^2) & A\lambda ^2 \\A\lambda ^3[1-(1-\frac{1}{2}\lambda ^2)(\rho +i\eta )]&-A\lambda ^2+\frac{1}{2}A\lambda ^4[1-2(\rho +i\eta )]& 1-\frac{1}{2}A^2\lambda ^4\end{pmatrix}.\) 
